In recent years, to cope with environmental problems on the global scale, and in order to prevent industrial wastes from contaminating the environment, reductions in a necessary heat quantity and a CO2 amount to be generated at the time of a thermal disposal have been attracting attention. As a result, there has been growing interest in recovery and recycling of materials.
Oxymethylene-based polymers are each an aliphatic ether type polymer or a polymer mainly composed of an aliphatic ether, and are each mainly derived from methanol as a raw material which a person can obtain without being in dependence on petroleum, so each of the polymers is considered to be a material that places a light load on an environment. The polymers are excellent materials that have been widely used in engineering plastics at present because of their high mechanical characteristics such as rigidity.
Known examples of the method of bonding resin materials each containing an oxymethylene-based polymer include: a method involving subjecting the materials to ultrasonic fusion in consideration of the fact that the surface of each of the materials is chemically inert; and a method involving roughening the surface of each of the oxymethylene-based polymers in advance or modifying the surface with an electron beam or by a plasma treatment in advance and bonding the materials with a cyanoacrylate-based adhesive or an epoxy-based adhesive. The former method requires a complicated step or a complicated facility, and is applicable only to part of the injection-molded articles. In addition, the latter method involves the following problems: the method cannot provide a sufficient bonding effect on the materials, and is not preferable in terms of recycling property because a component except the oxymethylene-based polymers must be used. In view of the foregoing, a technique for bonding resin materials each containing an oxymethylene-based polymer with a material composed of an oxymethylene-based polymer of the same kind has been desired.
The application of an oxymethylene-based amorphous copolymer (see Patent Document 1) or a copolymer having a low melting point (see Patent Document 2) to the bonding of oxymethylene-based polymers has been proposed. The application of the former material shows insufficient practicability because a bonding strength between the polymers is not sufficient, and the amorphous copolymer has so low a melting point that a product obtained after the bonding is poor in heat resistance. On the other hand, a bonding strength between the polymers in the case of the application of the latter material is significantly improved as compared to that in the case of the application of the former material, and a bonding component, that is, the latter material has improved heat resistance as compared to that of the former material, but a product obtained after the bonding is still so poor in heat resistance that the product cannot be used in the same environment as an environment where a conventional oxymethylene-based polymer has been used.
In addition, an oxymethylene-based polymer is a resin having high crystallinity, so the polymer involves the following problem: upon bonding of injection-molded articles, extrusion-molded articles, or stretched materials each containing the polymer, a heat history for the bonding at a high temperature or for a long period of time results in the thermal contraction of each of the polymers more than expected, and, furthermore, the melting of the raw material for any such article or material except the oxymethylene-based polymer cannot be ignored, with the result that a structure accurately maintaining its shape cannot be produced.
The inventors of the present invention have already developed an oxymethylene copolymer having a large comonomer content. The copolymer has a moderately low melting point as compared to that of the conventional oxymethylene copolymer, but the inventors have not referred to anything about the effectiveness of the copolymer as an adhesive (see Patent Document 3).
Patent Document 1: JP 01-132638 A
Patent Document 2: JP 08-60125 A
Patent Document 3: WO 2002-077049 A